Conventional steam cycle power plants using condensing steam turbines use steam extraction from the steam turbine to heat up boiler feed water to the appropriate temperature for use in the boiler.
In fossil fuel boilers, the appropriate temperature tends to be relatively high in order to avoid acid condensation at the entry/exit surfaces of the boiler.
Biomass fuel has the advantage of being virtually free of sulphur and other acidifying substances and so the risk of acid condensation is greatly reduced. The boiler vessel is pressurized and the flame temperature regulated in order to control NOx formation that may create a risk of acid condensation. Therefore, the deviation (condensation) point of the system remains at a relatively high temperature.
Modern boilers utilize energy from flue gases to the greatest extent possible. In circumstances where the flue gas is sufficiently free from acidifying substances, such as with biomass burning systems, and regulated flame temperature, the system may even provide for complete condensation of flue gas. Condensation of the flue gas provides an opportunity to utilize the latent heat of the fuel and allows for Low Heating Value (LHV) thermal efficiencies greater than 100%.
Nevertheless, despite the range of options available for producing power from steam cycle power plants there remains the desire to provide improvements in terms of efficiency, flexibility, emissions and scalability.
Environmental considerations especially in respect of carbon dioxide emissions are also increasingly relevant in terms of power plant design.